PROJECT SUMMARY Bacterial infections following childbirth, so-called puerperal infections, cause morbidity in 5 to 10% of all pregnant women globally. In most instances the infection is limited to the reproductive tract but at low frequency the infection spreads to the blood resulting in life-threatening sepsis, puerperal sepsis. Pathogens causing puerperal sepsis include the group A Streptococcus (GAS, S. pyogenes), which is the most common cause of severe maternal puerperal infections and death worldwide. GAS epidemiological data gained over the course of the last fifty years identifies a serotype-specific variability in the ability of GAS to cause disease. Of relevance to this proposal, serotype M28 GAS isolates are non-randomly associated with cases of puerperal sepsis. The molecular basis of why serotype M28 isolates cause puerperal sepsis at a significantly higher rate relative to those of other serotypes is to be investigated in this proposal. More specifically, the goal of the proposed research is to characterize whether the presence of a genomic island, termed `region of difference 2' (RD2), is key to the enhanced ability of serotype M28 GAS to cause puerperal sepsis. Sequence analysis of RD2 is consistent with this element being horizontally transferred into M28 GAS from group B Streptococci (GBS, S. agalactiae), an important finding given that GBS are a common constituent of the normal vaginal microflora and are also a major cause of neonatal invasive infections. Specific Aim 1: Test the hypothesis that RD2 enhances the ability of serotype M28 GAS isolates to both colonize the female reproductive tract and cause sepsis. To facilitate testing our hypothesis we recently constructed RD2 deletion mutant and complemented mutant derivatives of a representative M28 isolate. The parental, mutant, and complemented strains will be compared in tissue culture adherence assays, in growth assays using whole human blood (as a model of sepsis), and in a mouse model of vaginal colonization. Specific Aim 2: Test the hypothesis that the RD2 element alters the abundance of transcripts of core chromosomally-encoded virulence factors. Five putative transcription factors and two putative small regulatory RNAs are encoded within RD2. To test whether these putative regulators have targets outside of the RD2 region we will perform transcriptome comparisons between our parental and RD2 deletion mutant strains (via RNAseq). Comparisons will be performed following GAS growth in an ex vivo model of invasive infection. RNAseq data will be verified by targeted quantitative RT-PCR and Western analyses. Completion of the proposed research will advance our understanding of strain emergence and phenotypic heterogeneity in a prevalent Gram-positive pathogen. Specifically, the data would inform on the importance of RD2 with respect to the association of M28 GAS isolates with puerperal sepsis, and thereby provide a link between GAS gene content and clinical observations.